Alpha-methylene-gamma-butyrolactone and methyl alpha-methylene-gamma-butyrolactone are useful monomers in the preparation of both homopolymers and copolymers. In addition, the alpha-methylene-gamma-butyrolactone group is an important structural feature of many sesquiterpenes of biological importance.
Current ways of making alpha-methylene-gamma-butyrolactone monomer are unattractive because of low yields, byproducts formation and/or expensive starting materials.
In particular, U.S. Pat. No. 6,313,318 describes a method for converting certain starting lactones to alpha-methylene substituted lactones using a so-called basic catalyst that is made by treating silica with an inorganic salt of Ba, Mg, K, Cd, Rb, Na, Li, Sr, and La. A problem inherent in the method is that there is a significant decrease in the conversion of the starting lactone to the alpha-methylene product with time on stream (TOS).
US 2003-0166949 A1 describes a method for converting certain starting lactones to alpha-methylenelactones in a supercritical fluid (SCF) phase using a heterogeneous so-called basic catalyst that can be selected from the Group I, Group II, and Lanthanide Group oxides, hydroxides, carbonates, hydrogen carbonates, silicates, oxalates, carboxylates, acetates and phosphates, and mixtures thereof, any of which may be supported or unsupported. The basic catalyst may include additives and promoters to enhance catalyst efficiency. The method involves a reaction between the starting lactone and formaldehyde and may be carried out in a batch or continuous mode. The process can be run in either a single homogeneous phase over the catalyst, or the reactants and SCF may be in two different phases over the catalyst. The temperature of the reaction can range from about 70° C. to about 400° C., with a preferred range of about 100° C. to about 350° C. A more preferred range is about 200° C. to about 350° C. Pressure ranges are those required to achieve the supercritical or near-critical state under a given set of reaction conditions. The pressure of the reaction can range from about 5 to about 60 MPa, with a preferred range of about 15 to about 40 MPa.
One important measure of reactor performance that is a strong function of the catalyst activity is termed the “reactor productivity,” which can be expressed as the mass of product produced per mass of catalyst per unit of time. High and sustained reactor productivity is desired for a manufacturing process to improve economic viability. In addition, high catalyst activity (reactant conversion) is desirable, in general, to minimize additional processing required to separate the product from unconverted reactants. Although this performance parameter was not explicitly shown in the above-cited patent publication for the examples shown therein, the reactor productivity can be estimated from the data provided. Table 1 shows the variation in both catalyst activity (GVL conversion) and reactor productivity for the various examples conducted in continuous reactors. These data illustrate that problems inherent in the method include maximum sustained reactor productivities on the order of only 0.7 gram MeMBL/gram catalyst-hour and an undesirable decrease in activity with time on stream.
TABLE 1Reactor Productivity Estimatesfor Reference US 2003-0166949A1USCalculated2003-GVLReactor0166949A1CatalystWHSVConver-Productivity*ExampleCompo-(g GVL/TOSsion(g MeMBL/No.sitiong cat.-h)(h)(%)g cat.-h)15K2CO30.22—77.10.1916K2CO30.130.8432.90.051.0934.20.051.9333.30.052.4638.60.063.0040.20.061720%0.7—64.90.51K/SiO21820%0.7—78.40.61Rb/SiO21920%0.7—88.80.70Cs/SiO22020%0.7—69.20.54Cs/SiO22120%0.7—8.00.06Ca/SiO22220%0.7—31.50.25Ba/SiO22320%0.41.2589.90.40CSiO21.7588.50.402.2586.20.392.7583.80.383.0082.30.372420%0.71.4594.90.74Cs/SiO21.9590.30.712.4588.70.702.9586.00.673.2084.90.672520%0.71.3094.10.74Rb/SiO21.8092.80.732.3093.50.732.8094.60.743.3095.30.754.1094.90.742620%2.50.8072.82.04Rb/SiO21.0053.81.511.5037.11.042.0029.90.842.5027.20.763.0025.90.723.5024.80.694.0025.20.715.0026.30.745.5026.00.732720%0.71.2030.90.24Cs/SiO22.0030.60.242.5027.20.213.0026.00.203.5023.90.194.0022.10.172820%2.50.9017.90.50Rb/SiO21.205.10.141.600.80.021.900.60.022.400.30.012915%0.71.995.40.75Cs/SiO22.493.80.742.990.70.713.989.80.70(1st0.71.9062.40.49Regen.)2.5057.50.453.0055.20.43(2nd0.71.8063.40.50Regen.)2.5055.70.443.0054.10.423015%1.7—4.80.09Cs/SiO23120%1.1—28.70.35Rb/SiO2*Productivity estimated as product of WHSV, GVL Conversion, and Ratio of Molecular Weights of MeMBL/GVL (112.1/100.12) assuming 100% Selectivity to MeMBL.
It would be advantageous, therefore, to have a lactone conversion process that not only exhibits high initial activity (conversion), but also provides high reactor productivity (mass of product per mass of catalyst per unit of time) and sustained maintenance of a high level of activity and productivity with time on stream.